IgM and IgG antibody levels to ampicillin in patients with infectious mononucleosis.

By means of a sensitive radio-immunoassay an antibody-like activity against ampicillin was detected in both IgM and IgG immunoglobulin classes of patients with infectious mononucleosis, being fifteen times the level (for IgM) and six and a half times the level (for IgG) of control subjects. Such ampicillin antibody occurred without obvious relation to prior therapy with ampicillin. This antibody which may originate in a similar manner to Paul-Bunnell antibody was nevertheless immunologically unrelated. The possibility is discussed that the ampicillin rash in infectious mononucleosis results from a disseminated reaction of the small blood vessels to circulating ampicillin-antibody complexes.